This is what makes me sad that there will be no playable japanese subs. The Pacific is nice and U.S. subs are okay, but the technical specs from P-class to Gato are very similar and they 'feel' almost the same - an evolutionary design.
The only U.S. sub which were different are S-class, Argonaut, Nautilus and Barracuda - but they all don't make it into the game ...